Method of gluing thin wood veneer to a backing and flattening the veneer



Jan. 10, 1933. A. ELMENDORF 1,894,213

METHOD OF GLUING THIN woon VENEER TO A BACKING AND FLATTENING THE VENEER Original Filed July 10, 1931 Patented Jan. 10, 1933 UNITED STATES PATENT OFFICE ARMIN ELMENDORF, or CHICAGO, ILLINOIS, assrenon TO THE FLEXWOOD COMPANY,

A CORPORATION or DELAWARE METHOD OF GLUING THIN WOOD VENEER TO A BACKING AND FLATTENING THE VENEER Application filed July 10, 1931, Serial No. 549,951. Renewed October 5, 1932.

In the manufacture of so-called flexible or limp wood veneer attached to a flexible backing, the first step is to glue the veneer and the backing together. Veneers used for this purpose are very thin, their thickness ordinarily ranging from 1/100 of an inch to 1/40 of an inch, depending upon the kind of wood employed. There are various problems encountered in the gluing operation in order to obtain a successful glue joint and avoid stains on the exposed faces of the veneers. The most satisfactory process that I have heretofore employed, in the commercial manufacture of this product, is one in which the flexible backing of cloth or paper is coated with a thin layer of water-soluble glue which is then allowed to dry; the glue being softened through taking up moisture from the veneer which is either in a green state or is dampened to supply the requisite amount of moisture. Such veneers contain free moisture, and it is this moisture which softens the glue. The moisture in a sheet of green veneer is seldom uniformly distributed throughout the sheet. When there is considerable variation in the moisture content of green veneer, between different areas therein, care must be taken to insure good results in gluing; and, if the sheet should happen to be quite wet at one zone thereof and quite dry at another, there is danger that the glue will be softened to such an extent at the wet area that it strikes through the veneer. In the same way, if the veneer has been dried, and it is subsequently again moistened preparatory to the gluing operation, the moistening may not be done uniformly throughout the entire area of the sheet, and the veneer may, therefore, contain too much moisture at some points, resulting in the objectionable consequences just pointed out. These are, of course, extreme cases, although they do occur with sufiicient frequency to bring about a certain amount of waste. Also, where caustic glues are employed, as, for example, ordinary casein glue, whichrequire considerable moisture to become softened, it has been found that such glues generally stain the thin venear. I

The object'of the present invention is to that this is accomplished in a short period,

eliminate the objections to which I have just referred and make it possible to secure uniformity of gluing and a clean, unstained product by conducting the gluing operation in the same way in gluing all of the sheets of a given lot of veneer; thus making it unnecessary to give to the operation of gluing any one sheet of veneer more attention than is required for any other sheet.

I have discovered that there is suflicient hygroscopic moisture in the dry glue coating, or in dry veneer, or in both together, to so ten the glue to the extent required to unite the thin veneer and the backin if this moisture can be made available for the purpose. Therefore, the veneers employed in my improved process are dried until they contain no free moisture, but only moisture in a hygroscopic state, uniformly distributed, as is also the moisture content of the dry glue coat ing. I have found that, when the dry veneer is laid on the dry glue'coating on the backing under suflicient pressure to bring all parts of the veneer into intimate contact with the glue, and sufficient heat is applied quickly to vaporize some of the hygroscopic moisture content in the materials, the 'gluewill soften and a erfect joint will be secured without staining.

y vaporizing the moisture quickly, I mean O of from half a minute to perhaps five min- 8 utes, as distinguished from longer periods of hours or more. The higher the temperature, the shorter will be the time required to perform the gluing operation. The lower temperature limit may, therefore, be said to be that which will produce vaporization with sufficient rapidity to accomplish the intended purpose,whereas the upper limit is set by the character of the glue and cannot go to a temperature at which the glue might be injured. In actual practice, I have been able to secure satisfactory results with temperatures as low as 160 F. to 170 F. and with temperatures as high as 280 F. to 290 F. I

I have discovered that glue joints made in this way are at least fifty per cent stronger than when made in the old way. Therefore,

' viewed in one of its aspects, the present invention may be said to have for its object a 1 0 simple and novel process of gluing thin wood veneers to flexible backings in such a manner that the glue joints will be much stronger than those obtained through softening glues with water, in liquid form.

I have also discovered that, by my improved process, I am able to solve another vexatious problem quite separate from those involved in mere gluing operations. In drying from a green state, there is some shrinkage of wood in the direction of the grain, and this shrinkage is not uniform throughout a given piece of wood. In consequence of this characteristic of wood, it frequently happens that the unequal shrinkage lengthwise of the grain, in thin wood Veneers, produces what are known as cockles, namely, bulges in areas where there has been i'ess shrinkage than in the surrounding wood. Therefore, upon drying, veneers in which this unbalanced longitudinal shrinkage occurs will not present smooth, flat surfaces. While this characteristic of veneer is not objectionable in veneers that can be glued to rigid supporting surfaces under plate pressure, it is highly objectionable in the case of thin veneers glued to paper, cloth, or other flexible backings; for, when a piece of veneer of this kind is glued to a flexible backing, it draws the backingout of its flatshape and causes it to conform to the irregular configuration of the veneer. When an abnormal piece of veneer of this kind, provided with a flexible backing, is pasted or cemented to a wall, in the manner of wall paper, for example, the bulging portions will pull away from the wall even though they be flattened out during the pasting operation, and the wall covering will present a blistered appearance.

When my improved gluing process is carried out between hot plates, the bulges or cockles in the veneer are flattened into the plane of the sheet and, if the temperature be high enough and the heat and pressure are maintained for a sufficient length of time, the flattening of the bulges or cockles is found to have become permanent. While itmay be possible to reduce the cockles at the lower temperature limits noted above, I believe that the temperature should not be much below the boiling point of water. Good results have been obtained with temperatures around 200 F., although higher temperatures will produce results more quickly. In other 5 51words, although there is verylittle gain in the rapidity with which the gluing action is effected by using temperatures higher than the boiling point of water, a permanent flattening of the bulges or cockles in the veneer will be accomplished more rapidly as the temperature is increased, and it is, therefore, advantageous to use temperatures of from 250 F. to 280 F. when the veneer contains these bulges or cockles. v

varied, but I have found that it is better to use relatively high pressures. Thus, I have found that a better product is obtained by employing pressures of from 50 pounds to 200 pounds to the square inch than by pressures, say, of 10 pounds or 15 pounds.

It will thus be seen that, viewed in one of its aspects, my invention may be said to have for its object to insure the elimination of bulges or cockles in thin wood veneers by the mere operation of gluing them to flexible backings which, of themselves, would not have the capacity to hold the veneers flat.

Ordinarily the veneers employed in my process are air-dry and contain only the hygroscopic moisture determined bythe prevailing atmospheric humidity; but it is possible, in some instances, to produce a glued joint by utilizing simply the hygroscopic moisture in the glue, the veneer being dried to such a de ree as to contain no substantial amount of moisture, even in hygroscopic form. There would usually be no good purpose served in drying the veneer to a point where it has lost substantially all of its hygroscopic moisture, and I refer to that condition merely as a possibility and to demonstrate that, in carrying out my process, the hygroscopic moisture in both the veneer and the glue is or may be utilized to soften the lue. D The chief benefit of my improvement, so far as mere gluing is concerned, lies probably in the uniformity in the softening of the glue throughout the entire glue coating resulting in uniformity of the glue bond that is produced; together with the avoidance of the danger that the glue will be softened to an extent that will make it strike through very thin veneers and produce stains. There is another advantage, however, so far as mere gluing is concerned, and that is that I am able to employ glues which it has heretofore been necessary to avoid. Some glues, such as casein glues, after having been s read in the form of a coating and dried, require considerable moisture to dissolve and soften them. Where this moisture is supplied from wet veneer, the caustic in the glue almost always stains the veneer. With my improved process, these glues may be successfully employed if the dry veneers contain a large amount of hygroscopic moisture.

The hygroscopic moisture content of airdry veneers will ordinarily run from 6% to 18%, depending upon the prevailing atmospheric humidity. By controlling the hygroscopic moisture content of the veneer, 1t is possible to insure the presence of sufficient moisture to soften casein and similar glues to which I'have just referred, without making them so liquid that they will strike through and without bringing the caustic of the glue into action. In other words, if the veneers ar'esimply dried to a point where most of the hygroscopic moisture'remains, satisfactory gluing results without staining theveneer.

The various featuresof novelty whereby my invention is characterized will hereinafter be. pointed out with particularity in the claims; but, for a full understanding of my invention and of its objects and advantages, reference may be had to the following detailed description taken in connection with the accompanying drawing, wherein:

Figure 1" is a perspective view showing, on a greatly magnified scale, a fragment of flexi- 1 ble backing, a dry glue coating thereon, and a fragment of thin wood veneer lying upon the glue coating, preparatory to the gluing operation; Fig. 2 is a section, on a somewhat reduced scale, through a flexible backing and an overlying piece of veneer having bulges therein; Fig. 3 is. a section on line 33 of Fig. 2; Fig. 4 is a section through the hot press having therein the composite sheet of Figs. 2 and 3; and Fig. 5 is a-perspective View, T showing a' fragment of a backing sheet and a fragment of a sheet of veneer that has been glued thereto.

Referring to the drawing, '1 represents-a flexible sheet of cloth, paper, or other suitable material faced on one side with a thin glue coating 2 that-has been dried. 3 is a sheet of thin, dry wood veneer which is laid on the glue coating and united therewith by heated pressure. Where the veneer, in drying from a green state, has shrunk non-uniformly lengthwise of the grain, bulges, such as indicated at 4 and 5, will occur therein; these bulges being in areas where the shrinkage lengthwise of the grain has been less than 111 surrounding areas.

The composite sheet, consisting of the glueform of a roll, one end being drawn from the roll and placed in the press. After a sheet of veneer has been aflixed to that part of the backing in the press, as illustrated in Fig. 5, the press may be opened and another section of backing drawn into the press; whereupon another sheet of veneer may be laid on the backing with one edge abutting against the inner edge of the piece of veneer that has already been glued on. The press is then closed, to aflix the second sheet of veneer and reduce the cockles, if any be present, and the work is then shifted ahead so as to bring a th rd section of backing into the press. As the work leaves the press, it may be rolled up so that, after the entire backing strip has been covered with veneer, there remains a roll of composite material, with the grain of the veneer parallel to the axis of the roll, which is then carried to the flexing machine which works the composite sheet so as to render the veneer limp and flexible. The flexing of the veneer forms no part of the present invention, and-I mention it only because there is, from this point of view, some utility in rolling up the composite sheet.

- I claim:

1. The method of gluingto a flexible backing thin, dry wood veneer containing no free moisture, which consists in providing the backing with a dry coating of water-soluble glue, laying the veneer on the glue coating, and applying pressure and heat to bring the veneer into intimate contact with the glue and cause hygroscopic moisture in the work to vaporize, soften the glue and unite the veneer to the backing.

2. The method of gluing to a flexible backing thin, dry wood veneer containing only hygroscopic moisture, which consists in profaced backing and the dry veneer laid 'on theeviding a flexible backing with a water-solubacking, is placed between the upper and lowermembers A and B of a hot press, as shown in Fig. 4. The press is closed on the work and held closed. Where the veneer contains the bulges or cockles, a high temperature, preferably not much below the boiling point of water, and usually higher, is employed. Also, although the pressure need not always be great, Tprefer that the press shall exert on the work a pressure of from 50 pounds to 200 pounds per square inch. With the higher temperatures and pressures, the veneer will be effectively flattened out and united to the backing. The gluing action will be completed in a very short time, generally in a few seconds; but, if there are bulges or cockles present,.the press should remain closed for a longer period, perhaps five minutes or more. The press is then opened, and the work removed.

It will be seen that veneer in sheet form may be worked up into a composite product in the form of a long strip capable of being as rolled up. Thus,-the-backing may be in the ble glue coating that is dry and contains only hygroscopic moisture, laying the veneer on the glue coating, and applying pressure and heat to flatten the veneer and bring it into intimate contact with the glue, cause hygroscopic moisture in the work to vaporize and thus soften the glue and unite the veneer to the-backing, the degree of heat and the length of time of application thereof being suflicient to eliminate any bulges in the veneer due to unequal shrinkage along the grain ofthe wood.

3. The method of permanently flattening and gluing to a flexible backing thin, dry wood veneer containing no free moisture and having therein bulges caused by irregular shrinkage along the grain in drying from a green state, which consists in providing the backing with a dry coating of water-soluble glue, laying the veneer on the glue coating, and applying pressure to flatten the veneer not much lower than the boiling point of water.

4. The method of gluing to a flexible backing thin, dry, wood veneer containing no free moisture, and at'the same time permanently eliminating any bulges in the veneer due to unequal shrinkage in the direction of the grain in drying from a green state, which consists in providing a flexible backing with a water-soluble glue coating that is dry and contains only hygroscopic moisture, laying the veneer on the glue coating, and applying pressure to flatten the veneer and bring it into intimate contact with the glue, and heating the veneer and glue to a temperature at least approaching the boiling point of water, the pressure and heat being maintained for a period of several minutes.

5. The method of gluing to a flexible backing thin, dry wood veneer, which consists in providing the backing with a dry coating of water-soluble glue, laying the veneer on the glue coating, placing the composite sheet in a press, closing the press with a force suflicient to flatten the veneer and bring it into intimate contact with the glue, and applying through the press sufiicient heat quickly to vaporize the amount of hygroscopic moisture in the composite sheet required to soften the glue and cause it to unite the backing and the veneer.

6. The method of permanently flattening and gluing to a flexible backing thin, dry wood veneer having therein bulges produced by uneven shrinkage of the wood along the grain in drying from a green state, which consists in providing the backing with a dry coating of water-soluble glue, laying the veneer on the glue coating, placing the composite sheet in a press, closing the press with a force greater than that required to flatten the veneer, and applying through the press heat to raise the temperature of the veneer and glue to a point that at least approaches the boiling point of water, and maintaining the heat and pressure until the veneer remains permanently flat upon removing the composite sheet from the press.

7. The method of forminga long composite strip composed of a flexible backing and thin wood veneer glued thereto, which consists in providing a long strip of backing material q with a dry coating of water-soluble glue, laying on the strip a sheet of thin, dry wood veneer with the grain extending across the strip, pressing the veneer flat against the glue, applying heat quickly to vaporize hygroscopic moisture 1n the glue and the veneer, laying a second sheet of dry wood veneer on the backing in edge contact with the first sheet, and repeating the pressing and heating operation on the second sheet.

tion.

ARDEN ELMENDORF.

In testimony whereof, I sign this specifica- 

